Now we turn to the brand-new panda cub and the tricky medical exam. The cub was born on friday but it took almost two full days to get it checked out. Abc's matt gutman has more on the story. Reporter: The little cub was born squawking. And healthy at the smithsonian zoo in washington, d.C. Watch on panda cam as momma mei xiang scoops it up to nurse and nuzzles it. Due to a protective mother it took them more than 36 hours before they could finally examine it sunday. I actually had the cub in my hand and pulled it out and it started vocalizing. Reporter: The tiny cub the shape and weight of a stick of butter is strong but its gender will have to remain a mystery for another couple of weeks. The panda mei xiang gave birth to twins and the second was stillborn. They rarely survive in the wild so greeting this healthy cub with more than a little excitement. We have one that is doing well. Reporter: So happy because panda cubs are born entirely helpless, no eye, ears and fully dependent on their month but in the past two months they have delivered four cubs including the miraculous set of twins we met at zoo atlanta. This is extremely unusual. Very unusual. These are the only panda twins to ever survive in the united states. Reporter: Ever? Ever. Reporter: For the time being these tiny twin males will need constant supervision just like the little cub born in washington friday. Past the first week we get more and more optimistic. Reporter: They can't help but enjoy their fristiness and this -- brotherly, look at that. For "good morning america," matt gutman, abc news, miami. Are they the cutest? They are. Adorable. Oh.

This transcript has been automatically generated and may not be 100% accurate.

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